A turbine engine comprises one or more rotors formed of bladed disks, that is to say of blades mounted on a disk that is able to rotate about a shaft, and one or more vanes formed of bladed disks that are fixed, that is to say that do not rotate relative to the above shaft. The blades of the fixed and mobile disks are traversed by a gaseous fluid in a general direction parallel with the shaft. One of the main sources of excitation of the fixed or mobile blades originates from the wakes and from the pressure fluctuations generated by the obstacles adjacent to the blading. These various obstacles, namely the blades of the upstream and downstream stages, or else the casing arms induce turbulence in the flow of the fluid through the bladings. The movement of the blades in this turbulence creates a synchronous harmonic excitation of the rotation speed of the rotor and generates an instationary pressure field on the surface of the blade. The object of the present invention is therefore the attenuation of the impact of the interactions between two moveable bladed disks, one placed immediately downstream of the other and rotating in directions opposite to one another.
In the field of aviation turbine engines, the bladings are particularly sensitive parts because they must satisfy, in terms of design, imperatives of aerodynamic and aeroacoustic performance and of mechanical strength in rotation, temperature and aerodynamic load. All of these aspects mean that these structures are fairly statically loaded and that, because of the imperatives of service life, the amplitudes of vibrations that they sustain must remain low. Furthermore, the aeroelastic coupling, that is to say the coupling between the dynamics of the bladed disks and the fluid flow, is conditional upon the vibrational stability of the structure.
In the context of the design of a turbine engine, and because of the multidisciplinarity of those involved, the design process is iterative. The vibrational design is carried out in order to prevent the presence of critical resonances in the operating range of the machine. The assembly is validated at the end of the design cycle by an engine test in which the vibrational amplitudes are measured. High vibrational levels associated either with resonances or with vibrational instabilities sometimes occur. The fine-tuning of the rotor concerned must then be repeated, which is particularly protracted and costly.
The object of the present invention is to control, right at the design or development phase of the machine, the levels of vibrational response of the bladed disks in a turbine-engine structure comprising at least a first moveable bladed disk and a second moveable bladed disk which are contrarotating and traversed by a gaseous flow.